[Footnote 1:  Organic growth is the concentration of elements before diffused; cf. the union of nomadic families into settled tribes.]

Armed with these principles, however, Mr. Spencer advances to the discussion of the several divisions of “Special Philosophy.”  Passing over inorganic nature, he finds his task in the interpretation of the phenomena of life, mind, and society in terms of matter, motion, and force under the general evolution formula.  This procedure, however, must not be understood as in any wise materialistic.  Such an interpretation would be a misrepresentation, it is urged, for the strict relativity of the standpoint limits all conclusions to phenomena, and permits no inference concerning the nature of the “Unknowable.”  The Principles of Biology take up the phenomena of life.  Life is defined as the “continuous adjustment of internal relations to external relations.”  No attempt is made to explain its origin, yet (in the words of Mr. Sully) it is clear that the lowest forms of life are regarded as continuous in their essential nature with sub-vital processes.  The evolution of living organisms, from the lowest to the highest, with the development of all their parts and functions, results from the co-operation of various factors, external and internal, whose action is ultimately reducible to the universal law.

The field of psychology is intimately allied with biology, and yet istinguished from it.  Mental life is a subdivision of life in general, and may be subsumed under the general definition; but while biological truths concern the connection between internal phenomena, with but tacit or occasional recognition of the environment, psychology has to do neither with the internal connection nor the external connection, but “the connection between these two connections.”  Psychology in its subjective aspect, again, is a field entirely sui generis.  The substance of mind, conceived as the underlying substratum of mental states, is unknowable; but the character of those states of which mind, as we know it, is composed, is a legitimate subject of inquiry.  If this be carefully investigated, it seems highly probable that the ultimate unit of consciousness is something “of the same order as that which we call a nervous shock.”  Mind is proximately composed of feelings and the relations between feelings; from these, revived, associated, and integrated, the whole fabric of consciousness is built up.  There is, then, no sharp distinction between the several phases of mind.  If we trace its development objectively, in terms of the correspondence between inner and outer phenomena, we find a gradual progress from the less to the more complex, from the lower to the higher, without a break.  Reflex action, instinct, memory, reason, are simply stages in the process.  All is dependent on experience.  Even the forms of knowledge, which are a priori to the individual, are the product of experience in